Sprol

Photo Credit: NOAA, Great Lakes Environmental Research Laboratory

On November 7, 2006, Steve Pothoven and his fellow fisheries biologists with the National Oceanic and Atmospheric Administration spotted the latest invader of the North American Great Lakes. The invader is Hemimysis anomala, a half-inch long, bright orange shrimp native to the Black and Caspian Seas.

The Caspian shrimp joins 182 other invasive species, most brought to the Great Lakes in the ballast water of ocean-going shrimps, and a few migrating through the St. Lawrence Seaway. The sea lamprey caused the collapse of the lake trout population to one percent of its previous level in the 1950’s and 60’s, and is controlled at great expense today. The zebra mussel drives out indigenous species and clogs pipes, which then must be unclogged to the tune of a billion dollars a year.

What can we expect from this latest invader?

The new shrimp feeds very aggressively on the tiny plants and animals that comprise the lowest rung of the food chain.

Further, the shrimp are very different from native Great Lakes species. They will have a large impact on the Lakes’ ecology, because the more different an invader is, the more disruptive.

Photo Credit: NOAA, Great Lakes Environmental Research Laboratory

To prevent such invaders, ocean-going freighters that are headed for the Great Lakes must dump their ballast water and exchange it for sea water in the middle of the ocean. This pumps out most foreign fresh water critters, and the rest cannot survive in the sea water that is pumped in.

But, and it is a big but, fully loaded ships do not have to exchange their ballast water for sea water because they have little or no ballast water to begin with. Such ships make up about ninety percent of the overseas freighters that enter the Great Lakes.

The so-called “empty” ballast tanks are never quite empty. The shallow pools of water and muck make lovely homes for species such as our new Caspian shrimp. The Canadian government has recently begun to require all overseas ships to flush saltwater through their “empty” ballast tanks before they enter the St. Lawrence Seaway. This will hopefully help prevent additional invasive species from entering the Great Lakes, but will do little to mitigate the consequences of existing foreign< organisms that already call the lakes home.

Photo Credit: NOAA, Great Lakes Environmental Research Laboratory